Field of the Invention
The invention concerns a throttling valve for compressed air or the like and comprising a first valve component and a second valve component which together subtend an adjustable throttling gap, further an electric drive to displace at least one of the valve components for the purpose of adjusting the size of the throttling gap.
Electromagnetically driven throttling valves are already known, which comprise an armature fitted at its end with a plunger subtending a throttling gap together with a stationary component. The plunger-fitted armature can be displaced against a spring force by means of a current-fed coil. As a rule the spring biases the armature toward the closed position. The plunger position is controlled by changing the current in the coil. Thereupon the plunger assumes a position wherein the magnetic force and the spring force are balanced.
As regards such throttling valves, the plunger position and hence in fact the adjusted magnitude of the throttling gap depends on the tolerances for the spring constants and the tolerances affecting the magnetic drive. Most of the time comparatively complex control of the applied current is also required in order that a constant force be applied to the armature by means of a constant current into the coil regardless of coil temperature.
In such throttling valves, furthermore, the applied feed pressure of the compressed air and the flow of the compressed air through the throttling valve will affect the plunger position. This feature is especially disadvantageous when the feed pressure and/or the magnitude of the throttling aperture are changing.
Moreover such throttling valves evince hysteresis, and as a result the precise plunger position is determined not only by the coil current but also by the plunger's direction of motion.
Again the plunger position of such throttling valves will be affected by vibrations. Therefore such throttling valves are poorly suited for use in looms because looms generate vibrations by the beat motion of the reed and/or by displacements of the weaving frame.